Existing night vision goggles are complex electro-optical devices that intensify existing light instead of relying on their own light source. In a typical configuration, a conventional lens, called the objective lens, captures ambient light and some near-infrared light. The gathered light is then sent to an image-intensifier tube. The image-intensifier tube can use a photo cathode to convert the photons of light energy into electrons. As the electrons pass through the tube, more electrons can be released from atoms in the tube, multiplying the original number of electrons by a factor of thousands, often accomplished using a micro channel plate (MCP). The image-intensifier tube can be positioned such that cascaded electrons hit a screen coated with phosphors at the end of the tube where the electrons retain the position of the channel through which they passed. The energy of the electrons causes the phosphors to reach an excited state and release photons to create a green image on the screen that has come to characterize night vision. The green phosphor image can be viewed through an ocular lens where the image is magnified and focused.
Recently, light up-conversion devices have attracted a great deal of research interest because of their potential applications in night vision, range finding, and security, as well as semiconductor wafer inspections. Early near infrared (NIR) up-conversion devices were mostly based on the heterojunction structure of inorganic semiconductors where a photodetecting and a luminescent section are in series. The up-conversion devices are mainly distinguished by the method of photodetection. Up-conversion efficiencies of devices are typically very low. For example, one NIR-to-visible light up-conversion device that integrates a light-emitting diode (LED) with a semiconductor based photodetector exhibits a maximum external conversion efficiency of only 0.048 (4.8%) W/W. A hybrid organic/inorganic up-conversion device, where an InGaAs/InP photodetector is coupled to an organic light-emitting diode (OLED), exhibits an external conversion efficiency of 0.7% W/W. Currently inorganic and hybrid up-conversion devices are expensive to fabricate and the processes used for fabricating these devices arc not compatible with large area applications. Efforts are being made to achieve low cost up-conversion devices that have higher conversion efficiencies, although none has been identified that allows sufficient efficiency for a practical up-conversion device. Hence there remains a need to achieve higher efficiencies of an up-conversion device that can employ IR photodetector and light emitter materials that are currently available and can be fabricated in a cost effective manner.